JPS58677B2 - How to make a seal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency heating coil and a high frequency induction heat sealing method, and particularly to a high frequency heating coil and a high frequency induction heat sealing method with improved power factor.

The induction heating phenomenon in which a good conductor or magnetic material placed in an alternating magnetic field is heated by electromagnetic induction is well known, and several high-frequency heating devices using this heating phenomenon have been put into practical use.

A heat sealing process in manufacturing a storage container for cooked food and a heat sealing process in which the storage container is filled with cooked food and then sealed are known as suitable examples of use of the high frequency heating device.

A typical storage container is made of a triple-layered sheet made of aluminum or other metal foil laminated with a resin film on both sides, and after this sheet is shaped into a bag or other container shape, the joint is heat-sealed, leaving a portion behind. .

The storage container thus produced is filled with cooked food, and the filling opening is immediately heat-sealed.

Conventional heat sealing means is known to press a heating element against the sealing part and melt and bond the resin film at the joint part by heat conduction, but in order to prevent the resin film on the outside of the metal foil from melting Since the temperature of the heating element cannot be raised above a certain level, it takes a long time for the inner resin film that forms the joint to melt.

In particular, when high-temperature, short-time sterilization is performed in order not to impair the flavor of the food and to increase the efficiency of heat sterilization, the melting temperature of the inner resin film must be able to withstand high temperatures.
In addition, it is disadvantageous in terms of cost to make the outer resin film have a high melting temperature, so the difference in melting temperature between the inner and outer parts becomes smaller, and it takes a considerably longer time to melt the inner part. It takes.

In addition, it is preferable to use strong nylon as the inner resin film to prevent damage to the storage container, but nylon easily absorbs moisture due to its characteristics, so when melting and bonding the inner resin film, the nylon absorbs moisture. The water that has been evaporated will evaporate and the inner resin film will foam, so the temperature at the joint must be lowered to a temperature at which the evaporated water will be absorbed by the nylon again while the pressure remains in place.

If high frequency induction heating is used in such a heat sealing process, the metal foil of the sheet will be directly heated, the inner resin film will be effectively melted and bonded, and the work efficiency will be extremely improved.
If the supply of high-frequency power to the heating coil is stopped in the pressed state, the heat of the heated sheet is transferred to the lower temperature heating coil, and the above-mentioned foaming can also be suppressed.

When heat-sealing, the heating coil is pressed against the sheet, so the heating coil and the metal foil that is the object to be heated come very close to each other, and the mutual induction coefficient between the heating coil and the metal foil is large, and the power factor of the heating coil is low. used in high conditions.

In order to supply power to such a load with a high power factor, the most suitable high frequency power source is a switching type inverter using power transistors or SIRISK.

That is, this type of high-frequency power source does not require a large tank circuit like the vacuum tube oscillator type described above, so it can be small, low-speed, and highly efficient.

The power supply circuit for high frequency induction heating is preferably a high frequency power supply circuit using a switching type inverter that uses power transistors that are small in size and have high heating efficiency.

When power is supplied using such a transistor type power supply circuit, the maximum power that can be extracted increases as the power factor of the load increases.

In other words, the power supplied to the load is proportional to the product of voltage and current regulated by the breakdown limit of the drive transistor, but when the power factor of the load is low, the energy stored in the inductance of the load increases, and this storage Energy only travels back and forth between the power supply and the inductance each time the drive transistor switches, and cannot be converted into active power.

Therefore, a high-frequency induction heating device using a transistor power supply circuit requires a heating coil with a high power factor.In order to increase the power factor of the heating coil, the mutual induction coefficient between the heating coil and the heated object must be as close to 1 as possible. It is preferable to do so.

When heat sealing cooked food storage containers, it is relatively difficult to obtain heating coils with high power factors.

One difficulty arises from the fact that the heating when sealing the storage container must be formed in a narrow band.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a heating coil with a high power factor suitable for a high frequency heat sealing device.

The heating coil according to the present invention will be explained in detail below based on the drawings.

FIG. 1 shows the basic flat spiral coil shape of an ordinary heating coil.

This heating coil 10 is pressed against the object to be heated in an insulated state, and a portion corresponding to the shape of the coil is heated.

FIG. 2 shows an intermediate stage of manufacturing a bag-like storage container, in which two laminated sheets 11 made of metal foils such as aluminum are laminated with resin films on both sides, and a heating coil 10 is placed on top of the laminated sheets 11. By moving in the direction of the arrow, the joint portion 12 shown by diagonal lines is heat-sealed.

Then, by cutting the joint 12 as shown by the chain line, a bag-shaped storage container with three sides joined can be obtained.

At the time of this manufacture, the flat spiral coil 10 shown in FIG. 1 cannot be used because, as is clear from the slightly exaggerated view of FIG. 2, the portion shown by the broken line is heat-sealed.

For this reason, in actual use, it is probably necessary to separate one side 10A of the heating coil 10 from the laminated sheet 11, which is the object to be heated, so as to make it an ineffective side.

FIG. 3 shows a state in which the storage container manufactured as described in FIG. 2 is filled with cooked food and then the opening 13 is heated and sealed by the heating coil 10.

Even in this case, it is easily understood that the ineffective side 10A of the heating coil 10 does not come close to the object to be heated.

In a heating coil having such an ineffective side, the ineffective side does not electromagnetically couple with the object to be heated, so the mutual induction coefficient decreases, and it is impossible to obtain a heating coil with a high power factor.

In FIG. 1, it appears that by bringing the ineffective side 10A of the heating coil 10 close to the heating side 10B, one narrow band-shaped heating seal is achieved.

However, more realistically, this idea would be rejected because the mutual induction coefficient itself would decrease as a result.

FIG. 4 shows a conventional improved heating coil for airtightly sealing the opening of a storage container, in which a ferrite magnetic core 14 is fixed to a flat spiral coil 10.

In this conventional example, most of the magnetic flux generated from the heating coil 10 passes through the magnetic core 14 as shown by arrow P, contributing to an increase in the mutual induction coefficient.

However, even in this case, the mutual induction coefficient of the entire heating coil is suppressed due to the presence of the magnetic flux Q that does not interlink with the heated body due to the ineffective side 10A.

FIG. 5 shows a schematic configuration diagram of a high frequency heating coil according to the present invention, in which a short circuit coil 15 is provided to reduce leakage magnetic flux Q that interlinks only with the ineffective side 10A.

The short circuit coil 15 is arranged so that one side thereof is close to the ineffective side 10A of the heating coil 10, and forms a short circuit current path surrounding the magnetic circuit of the magnetic core 14.

When the short circuit coil 15 is provided as shown, the leakage magnetic flux Q
interlinks with the short-circuited coil 15, so a current flows in the short-circuited coil 15 in a direction that cancels out this leakage magnetic flux Q, as shown in the figure.

As a result, it is understood that the leakage magnetic flux Q is canceled out by the short-circuited coil 15, and the mutual induction coefficient of the heating coils increases.

The reason why the shorting coil 15 is provided so as to surround the magnetic circuit of the magnetic core 14 is to maximize the electromagnetic coupling with the leakage magnetic flux Q.

In other words, the leakage magnetic flux Q formed by the ineffective side 10A is
Since substantially everything passes through the magnetic core 14, the magnetic core 14
By surrounding the two to form a short-circuit current path, the electromagnetic coupling described above can be easily maximized.

However, the present invention is not limited to this, and any structure may be used as long as a short-circuit current path that is interlinked with the leakage magnetic flux Q and sufficiently electromagnetically coupled is formed.

In the embodiment of FIG. 5, the shorting coil 15 consists of a wound coil of copper wire, but it is also possible to form a substantially annular shorting current path with a conductive metal plate.

An embodiment in which a metal mount for fixing a heating coil also serves as a short-circuiting coil is shown in FIGS. 6 and 7.

In this embodiment, the mount 16 is made of brass, which has high electrical conductivity and mechanical strength and is easy to process, and serves as a shorting coil.

The mounting base 16 consists of a rod having a substantially U-shaped cross section,
As shown in FIG. 7, it is firmly fixed to the movable arm 17 of the storage container heat sealing machine with screws 18 and 19.

A magnetic core 14 made of ferrite and having a U-shaped cross section is fixed in the longitudinal direction of the mounting base 16.

A heater 20 is further embedded in the magnetic core 14, and this heater 20 prevents the heating coil device itself from absorbing heat from the storage container so that the storage container and the heating coil device come into contact during the heat sealing process of the storage container. do.

This heater 20 is extremely suitable for a contact type high-frequency induction heating device, and if this heater 20 is not provided, a situation may occur in which the surrounding area of the desired seal portion is also heated unnecessarily. Dew.

The heating side 10B of the heating coil 10 is fixed to the front surface of the heater 20, and the ineffective side 10A thereof is fixed to the mounting base 16, so that the heating coil 10 is arranged so as to surround the magnetic core 14.

In this state, the mounting base 16 is attached to the side 1 that is close to the invalid side 10A.
6A and the opposite end 16B form a short-circuit current path surrounding the magnetic circuit of the magnetic core 14, and absorb the leakage magnetic flux due to the ineffective side 10A.

Copper protection plates 21 and 22 are fixed to the front surfaces of the heating side 10B and the ineffective side 10A of the heating coil 10, and the heating coil 1
0 from being damaged.

FIG. 8 shows another embodiment of the present invention, in which the heating coil 1
A state in which the ineffective side 10A of 0 is bent at 90 degrees with respect to the heating side 10B and fixed to the mounting base 16 is shown.

According to this embodiment, the heating coil device can be miniaturized, and the mutual induction coefficient between the ineffective side 10A of the heating coil 10 and the object to be heated is small, so that a band-shaped seal is performed during bag making as shown in Fig. 2. There is an advantage that it can be done.

FIG. 9 shows still another embodiment of the present invention, in which the ineffective side 10A of the heating coil is located on the opposite side of the heating side 10B with the heater 20 in between.

An opening 16a is formed in a part of the mounting base 16, and the invalid side 10A is inserted into this opening 16a.

According to this embodiment, the heating coil device can be miniaturized and the mutual induction coefficient between the ineffective side 10A of the heating coil 10 and the object to be heated is extremely small, so that a band-shaped seal is performed during bag making as shown in FIG. This is particularly preferable.

When performing sealing by high-frequency induction heating using the heating coil according to the present invention, there are two methods: as described above, two substantially identical heating coils are used to press the sealing part with the heating side of the heating coil, and one method is used. There is a method in which the heating side of the heating coil is pressed against the sealing part, and the magnetic core that is to form a magnetic circuit with the magnetic core of the heating coil is placed on the opposite side, but there is not much difference in the heating characteristics of the two. do not have.

The high-frequency induction heating coil of the present invention increases the mutual induction coefficient between the heating side and the object to be heated, reduces the mutual induction coefficient between the ineffective side and the object to be heated, and increases the current density in the desired heating area. It is a highly efficient coil for high-frequency induction heating sealing because it lowers the current density in other parts and reduces the leakage magnetic flux generated at the ineffective side by the short-circuiting coil, and has a high power factor.

Next, we will explain how to use this high-frequency induction heating coil to seal a sheet that has a hygroscopic resin film such as nylon on the inside of the metal foil.

According to this heating coil, only the desired portion can be effectively heated, so that a good seal can be obtained even if the heating temperature of the heater that heats only the heating piece described above is not so high.

Therefore, when sealing a sheet containing a hygroscopic resin, high-frequency power is supplied after the heating coil presses the sealed portion, and once the seal portion has melted, the supply of high-frequency power is stopped.

At the temperature at which the seal part melts, the water absorbed in the resin film evaporates and the seal part foams, but when the high-frequency power supply is stopped, the temperature of the seal part moves to the lower temperature heating coil, causing the seal part to melt. Foaming disappears.

When the temperature of the seal part has decreased sufficiently, it is sufficient to stop pressing the seal part by the heating coil.

Even in this case, since the higher the temperature of the heating piece of the coil, the more efficient heating can be performed, it is preferable to keep the temperature at a high temperature to such an extent that no foaming is observed after the sealing part has finished sealing.

As explained above, according to the high frequency induction heating coil according to the present invention, an extremely high power factor can be obtained.

The power factor of the coil according to the present invention can be universally set to a value of 0.9 or more, and the power factor value of the conventional general induction coil is 0.
．． It is clear that the improvement has an extremely large effect compared to the case where the value is 1 or less.

A high power factor heating coil can dramatically improve its heating efficiency.

That is, since the electric power supplied to the object to be heated is proportional to the power factor of the heating coil, when the same electric power is supplied to the object to be heated, the current value can be reduced in a heating coil with a high power factor.

Reducing the current value of the heating coil offers various advantages in the fabrication of high frequency induction heating devices.

This can be understood from the fact that the heating coil of the present invention has a power factor of 10 times or more and a current value of 1/10 or less compared to the conventional heating coil.

These values mean that the heating coil wire diameter for supplying the same electric power can be reduced to 1/10 or less, and this point is extremely important.

Reducing the diameter of the heating coil wire makes it easier to form the heating coil into an arbitrary shape.

Further, the reduction in the current value has the advantage that the structure of the conducting wire portion can be simplified, and furthermore, the conducting wire can be made thinner and no cooling device is required.

This has the advantage that a flexible conducting wire with a small diameter can be used especially in a device in which the heating coil must be movable.

As a power supply circuit suitable for the high-frequency heating coil according to the present invention, a small and low-order power supply circuit for a high-frequency heating device that can obtain high-efficiency, high-output high-frequency power using a power transistor or a SIRISK is suitable.

FIG. 10 shows the basic configuration of a power supply circuit used in the present invention.

The output transformer 210 has a primary winding 211 and a secondary winding 212.
The primary winding 211 has an intermediate tap 213 connected to a power supply circuit 220.

The secondary winding 212 of the output transformer 210 is connected to a high frequency heating coil according to the invention.

The power supply circuit 220 includes a commercial power supply 221 and a full-wave rectifier circuit 222
and a high-frequency bypass capacitor 223 , and applies full-wave rectified power to the intermediate tap 213 of the output transformer 210 .

At both ends of the primary winding 211 of the output transformer 210, the output transistor circuits 230 and 240 include output transistors 231 and 241, current limiting resistors 232 and 242, and
Includes reactive power return diodes 233 and 243.

The collectors of the output transistors 231 and 241 are respectively connected to both ends of the primary winding 211, and a signal from the oscillation circuit 250 is amplified by the drive circuits 234 and 244 and applied to their bases.

Note that the transistors 235, 236, 245 and 246 of the drive circuit are used in a saturated state.

The collector of the output transistor 231 is a feedback circuit 271,
It is connected to the base of the output transistor 241 via a drive circuit 244, and similarly, the collector of the output transistor 241 is connected to the base of the output transistor 231 via a feedback circuit 272 and a drive circuit 234.

In this embodiment, the drive circuits 234, 244 receive the feedback signal 3
The transistors 71 and 372 are provided in order to reduce the power loss that occurs because they are applied from points a and b, which have fairly high voltages, and the transistors in this circuit are used in a saturated state.

That is, since the base voltages of the output transistors 231 and 241 need only be low, drive circuits 234 and 244 with low power supply voltages +E and -E are provided, and the current of the feedback signals 371 and 372 is passed through the drive circuits 234 and 244. By amplifying the feedback signals 371 and 372, the current values of the feedback signals 371 and 372 can be reduced, thereby reducing power loss in the feedback resistors 111 and 112.

The drive circuits 234 and 244 include NPN transistors 235 and 245 to which a positive voltage +E is applied to the collector, and a PNP transistor 236°2 to which a negative voltage -E is applied to the collector.
46.

The drive circuits 234 and 244 include control transistors 277 .
278 are connected, and these control transistors 277 .
278 is normally held off, but turns on during power control or overcurrent protection.

A power control signal c, an overcurrent protection signal d and a zero volt start signal e are applied to the bases of each of the control transistors 277, 278.

Zero volt start signal e is turned off, and intermediate tap 2
The pulsating voltage of 13 is sufficient to turn on the output transistor 231241, and the output transistors 231, 24
1 is undefined, but for example, if the output j of the square wave generator forming the oscillation circuit 250 is positive, the output transistor 2
31 is turned on.

Then, the voltage at the collector a of the output transistor 231 becomes zero, and the voltage at the collector b of the output transistor 240 becomes twice the voltage at the intermediate tap 213 due to the transformer action of the output transistor.

Therefore, output transistor 231 is kept on and output transistor 241 is kept off.

When the output j of the square wave generator eventually becomes negative and the output k becomes positive, the drive signal for the output transistor 231 turns off, but there is a slight delay in turning off the output transistor 231 due to the accumulated charge, and eventually the output transistor 23
1 turns off, the collector a of the output transistor 231 becomes positive, the feedback signal 372 is amplified by the drive circuit 244, and the output transistor 241 is turned on.

As described above, after confirming the OFF operation of one output transistor, the output transistor of the other output transistor is turned ON, so that the two transistor circuits do not operate at the same time, and current spikes etc. that adversely affect the circuit occur. This prevents damage to the drive transistor and the like.

[Brief explanation of the drawings] Fig. 1 is a schematic diagram showing the basic flat spiral coil shape of a normal heating coil, and Fig. 2 is a plan view showing the process of manufacturing a bag-shaped storage container using the heating coil shown in Fig. 1. 3 is a plan view showing the process of airtightly sealing the opening of a bag-like storage container using the heating coil shown in FIG. 1, FIG. 4 is a schematic diagram showing a conventional heating coil, and FIG. FIG. 6 is a perspective view showing a preferred embodiment of the high-frequency heating coil according to the present invention, FIG. 7 is a sectional view of FIG. 6, and FIG. FIG. 9 is a sectional view showing still another embodiment of the present invention, and FIG. 10 is a power supply circuit diagram suitable for the present invention. 10... Heating coil, 10A... Ineffective side, 10B... Heating side, 14... Magnetic core, 15... Short circuit coil.

Claims (1)

[Scope of Claims] 1. A high-frequency heating coil having a heating side disposed close to an object to be heated and an ineffective side forming a current return path, and a U-shaped magnetic core supporting the heating side. The magnetic core is arranged so as to surround the heating side, and the magnetic path end face position coincides with the heating side position, and the magnetic core is arranged close to the ineffective side of the high frequency heating coil. 1. A high-frequency heating coil comprising a substantially annular short-circuit current path member having a substantial current path portion and interlinked only with the magnetic flux formed by the ineffective side. 2. The process of pressing the high-frequency heating coil including the heated side and the ineffective side against the heated body and inductively heating only the sealed part of the heated body corresponding to the heated side, and applying the high-frequency current of the heating coil after completing the melting and joining of the sealed part. A high-frequency induction heating sealing method including a step of shutting off and a cooling step of pressing and holding a heating coil against an object to be heated while the temperature of the seal portion decreases to a predetermined temperature.